Apex domains cannot have CNAME records.
Question and response
Question
dig read-books.org. NS
Answer
read-books.org. 5 NS nf3.no-ip.com.
read-books.org. 5 NS nf1.no-ip.com.
read-books.org. 5 NS nf5.no-ip.com.
read-books.org. 5 NS nf2.no-ip.com.
read-books.org. 5 NS nf4.no-ip.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0